1. Field of the Invention
This invention relates to dynamoelectric machines and more particularly to terminal boxes for high voltage bushings employed with such machines.
2. Description of the Prior Art
Stray magnetic flux from the phase leads and neutral leads carried through the terminal box of a dynamoelectric machine by the high voltage bushings may, in the absence of appropriate shielding, impinge upon the walls of the terminal box and cause circulating currents therein. This can result in substantial undesirable heating of the terminal box walls.
Flux shields have been employed in the prior art to reduce the amount of stray flux impinging on the wall of the terminal box and hence to reduce the heating of the terminal box. One such prior art flux shield is shown in U.S. Pat. No. 3,808,489 - Albright et al., which is assigned to the assignee of the present invention. The structure shown in the Albright et al. patent effects substantial shielding and significantly reduces the temperature which would otherwise be present in the wall of the terminal box. The Albright et al. structure does not, however, achieve optimal results in this respect, in part because necessary passages for flow of cooling fluid provide openings for direct transmission of flux from the bushings to the wall of the terminal box, in part because of the fact that only a single flux shield of a single material is used, and in part, because the coolant flow paths do not provide optimum cooling to the portions of the terminal box wall susceptible to the greatest heating. By the present invention, these shortcomings of the aforementioned prior art structure are overcome and a flux shielding arrangement is provided which precludes any direct transmission of the stray flux from the bushing area to the wall of the terminal box and which, by using multiple shields and by using different kinds of material for the multiple shields employed, achieves improved shielding. Additionally the coolant flow is direct at higher velocity over the regions of highest heating and improved cooling thereat is achieved.
Accordingly, it is an object of this invention to provide an improved terminal box structure for dynamoelectric machines which reduces the heating of the walls of the terminal box.
It is another object of this invention to provide an improved flux shielding arrangement for the terminal box of such machines.
It is still another object of the invention to provide maximum cooling fluid velocity in regions of maximum heating susceptibility.